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(No Model.)

E. W. R Jr. GOMMUTAT RUSH. N0. 447,352. Patented Mar. 3,1891.

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UNITED STATES PATENT OFFICE.

EDIVIN IVIIIBUR RICE, JR., CF LYNN, MASSACHUSETTS, ASSIGNCR TO THE THOMSON-HOUSTON ELECTRIC COMPANY, CF CONNECTICUT.

COMM UTATOR-BRUSH.

SPECIFICATION forming' part Of Letters Patent NO. 447,352, dated March 3, 1891.

Application filed November 2S, 1890. Serial No. 372,859 (No model.)

To all whom it may concern:

Be it known that I, EDWIN WILBUE RICE, Jr., acitizen of the United States, residing at Lynn, county of Essex, and State of Massachusetts, have invented a certain new and useful Improvement in Commutator-Brushes, of which the following is a specification.

My present invention relates to carbon commutatorbrushes for dynamo electric Inachines; and it consists in providing such a brush with a coating of metal gradually decreasing in thickness toward its wearing-sun face, for I have found that such a coating gives the brush all the advantages gained by the metal coating' of brushes now in use, and, furthermore, avoids peeling of the coating from the carbon with the evil results incident thereto, which have proved heretofore a serious defect.

It has been customary to cover a carbon brush with a coating of copper of uniform thickness,as indicated in Figures 4: and 5 of the accompanying' drawings, for securing a coin-- paratively high degree of conductivity and avoiding heating. Upon using' these brushes, however, it is found that the lower portions of the coating will peel off from the carbon, forming a rough jagged Wearing-edge, liable to cause short circuits in the machine, poor contacts, and to interfere with freedom of play of the brush in its holder. This peeling is what I now aim to avoid, and I have found that it can be done by gradually decreasing the thickness of the Inetal coating, so that at the wearing-surface of the brush the coating" is very thin, practically no Inore than a metal iilm. It will then wear oit' smoothly and does not readily become caught, thereby stripping or peeling the coating.

These improvements are illustrated in the accompanying drawings, wherein- Figs. l, 2, and 3 are respectively sections taken through one of my improved brushes with the metal coating applied in slightlymodified ways; and Figs. 4 and 5 illustrate in perspective and in section an old form of comnIutator-brush upon which my invention is au improvement.

In the drawings, A represents a carbon connnutator-bi'ush similar to those now in use,

and B the metal coating. In Fig'. l this coating tapers uniformly from one end of the brush nearly down to its wearing-surface, while in Fig'. 2 the coating is of uniform thickness to a point at about the middle of the brush, and from there on tapers down, so that the thickness of the coating' is gradually decreased, terminating at a, as before, in a mere film. Fig. 3 shows a similarcoating of gradually-decreasing thickness; but in this modi- 6c iication the coating resembles a succession of layers of varying and graduallydecreasing thickness. This arrangement, while the same in idea, is not considered so good as that in either of the preceding figures, for the increase in conductivity and thickness of the metal is not uniform.

The coating 'can best be applied as a plating of copper and the variations in thickness gained in a number of ways. For instance, 7o the brush can be placed in the plating-bath and gradually raised out of it manually or automatically, so that the portions of the brush where a heavy coating is desired would be the longest in the bath; or the brush may simply be arranged in the copper bath with that part which is to have a thick plating nearest the copper electrode; or, again, a plating of uniform thickness could be applied and portions dissolved by acid to gain the 8o desired thinness. The first method is the one I consider preferable.

In Figs. et and 5 the old plating of uniform thickness is represented at C, and the jagged lower edge 'formed by peeling of the coating' is shown much as it appears in actual practice. By my improvements this is all avoided and without sacrificing any of the other functions for which such a coating is used. The thin portion of the coating adheres closely 9o and firmly to the carbon and wears away smoothly, while the thick upper portion is suiiicient to keep down the resistance of the brush and avoid heating'.

I claim- 9 5 l. A carbon comnIutator-brush having a metal coating gradually decreasing' in thickness toward the wearing-surface of the brush, for the purpose set forth.

2. A carbon commutator-brush coated with Ioo a plating of copper gradually decreasing in thickness toward the Wearingsurface of the brush.

3. A carbon commutator-brush coated with 5 a plating of metal tapering down toward the v Wearing-surface of the brush until it terminates in practically a mere lm, as set fort-h.

In testimony whereof I have hereto set my hand this 25th day of November, 1890.

EDWIN WILBUR RICE, JR.

Witnesses:

JOHN W. GIBBONEY, l ELIHU THOMSON. 

